1. Field of the Invention
Embodiments of the present invention relate to a peripheral device for using the dual bus interface in an ExpressCard slot, and a method of using same.
2. Description of the Related Art
The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large storage capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
One popular type of flash memory device is the CompactFlash® memory card manufactured by SanDisk Corporation, Milpitas, Calif. While used in a variety of different applications, the CompactFlash memory card has been adopted as the de facto standard in the professional and consumer imaging markets. While there are several reasons why this is so, including the large storage capacity and low cost per megabyte, the form factor of the CompactFlash memory card has proven to be a significant contributing factor. At 43 mm by 36 mm, the card is large enough for easy manipulation, yet small enough for convenient transport and use in current high resolution digital cameras. Professionals and consumers are comfortable with and have grown accustomed to this size memory card.
A few years ago, a coalition of member companies of the Personal Computer Memory Card International Association (PCMCIA) developed the ExpressCard® peripheral as a new standard for PC Card technology. FIG. 1 shows a pair of ExpressCard memory cards 20 and 22 according to the two standard ExpressCard form factors. ExpressCard module 20 has a length of 75 mm and a largest width of 54 mm. ExpressCard module 22 has a length of 75 mm and a width of 34 mm. Both formats are 5 mm thick.
Module 20 is configured under the standard to be received within an ExpressCard slot 24. Module 22 is configured to be received within either slot 24 or a narrower slot 26. In particular, slot 24 includes a guide 28 to steer the module 22 into the correct position to ensure proper nesting of the module 22 upon insertion into the wider slot 24.
One of the advantages of the ExpressCard format over the older PC Card format is the improved data transfer speed due to the use of higher performance serial data interfaces rather than parallel buses. ExpressCard technology uses a simpler connector and eliminates the CardBus controller in PC Card applications by using direct connections to PCI-Express (PCIe) and USB ports in the host platform 30. This lowers the cost of slot implementations in the host platform. However, in order to comply with the ExpressCard standard, it is a requirement that a host platform 30 must support both the PCIe and USB interfaces. This includes a single PCIe lane (×1) operating at the baseline 2.5 Gbps data rate, in each direction, as defined in the PCI Express Base Specification 1.0a by the PCI-SIG, which specification is incorporated herein by reference in its entirety. The host interface must also support the low-, full- and high-speed USB data rates as defined by the USB 2.0 Specification of the USB Implementers Forum, which specification is also incorporated herein by reference in its entirety.
Due to space and cost constraints, host computing platforms 30 typically only include a single ExpressCard slot. In platforms having only a single ExpressCard slot, when an ExpressCard module 20/22 is inserted into the slot, the slot is then no longer available to perform any other functions. This is so despite the fact that the interface has two independent buses—the high performance PCIe bus and the more common USB interface. At present, there are no known peripheral devices that leverage both buses within the same ExpressCard slot.